1. Field of the Invention
The present invention pertains to a method and apparatus for transportation of hydrocarbons through subsea pipelines from producing oil and gas fields to gathering and treating facilities remote from the production fields.
2. The Prior Art
One of the biggest problems associated with offshore production of oil and gas is the transportation of hydrocarbon gas and liquid mixtures from subsea wells to production facilities, either on platforms or ashore, through subsea pipelines over distances greater than 10 to 15 miles. Among the problems which must be overcome are the pressure to move the oil and gas as well as to keep the pipelines open to flow. The cold of the subsea environment and/or inadequate flow rates can cause the build up of hydrates on the walls of the pipeline to eventually stop flow altogether. Without some mechanism to impart a pressure head to the oil and gas, it becomes impracticable to move significant volumes of oil and gas further than relatively short distances, on the order of less than a couple of miles. It is, of course, possible to provide the pipeline with subsea pumps. However, the costs of such pumps, which must be constructed to both operate in the harsh subsea environment as well as to handle multiphase flow, is very high raising substantial questions of the economies of pumps as a solution to the problem.
The oil and gas industry is investigating a number of systems having as a goal to achieve a pressure boost enabling the subsea movement of oil and gas over greater distances. The systems being studied include above mentioned subsea multiphase pumps, such as the PLC by Multiphase Systems of U.K., and conventional single phase pumps, such as the GA-SP pump by Goodfellow Projects of Houston, Tex. The latter pumps are somewhat less expensive than multiphase pumps, but they must be inserted into the pipeline after separation of the fluid phases to liquid and gas phases, with the liquid and gas phase streams subsequently being recombined before delivery into the transportation pipeline in multiphase flow.